Different types of magnetic recording mediums are used in various fields, for example, video tapes, audio tapes and computers, since they have various excellent recording characteristics, and are superior to any other recording systems. For instance, the characteristics are such that repeated use of the medium is possible, that conversion of signals into electronic codes is easy so that construction of systems in combination with peripheral electronic devices is possible, and that correction of signals may be effected simply. Further improvement and elevation of the recording density of such a recording medium has heretofore been always desired in order to satisfy the current requirements of provision of small-sized devices, elevation of the quality of recording and reproducing signals, prolongation of the time of recording and enlargement of the recording capacity.
For this reason, various means have been tried, including the improvement of magnetic powders (substances) themselves, improvement of the surface property of the magnetic layer, and improvement of the dispersibility and the degree of filling (i.e., packing density) of magnetic powders in the magnetic layer.
In order to elevate the output by reducing the thickness loss and self-demagnetization during recording and reproduction, reducing the thickness of the magnetic layer to 1.0 .mu.m or less is known to be effective for elevating the density and capacity scales of a magnetic recording medium. In particular, reduction of the thickness of the magnetic layer has come to be important in the field of video tapes for providing VTR video tapes applicable to high-vision VTR devices, reduction in thickness is also important in the field of magnetic recording discs for digital recording, such as floppy discs which recently must have a high capacity of 10 M bytes or more with the recent popularity of personal computers. This is because of the elevation of the capacity of application software and increase of the information data to be processed, especially for elevating the capacity of the magnetic recording medium in accordance with the reduction of the track width of the magnetic head in view of the necessity of elevation of the output and of improvement of the overwriting characteristic. In a magnetic recording medium for computers such as floppy discs, overwriting of recording signals each having a different magnetic wavelength is necessary. For this, heretofore, overwriting of two kinds of signals, the if signal and the 2f signal, which are in such a relation that the frequency of the latter is two times of that of the former, has been considered to be satisfactory. However, for high-capacity magnetic recording discs of 10 M bytes or more which have recently been in demand, not only shortening of the recording wavelength but also overwriting of plural signals falling a broad range of the frequency ratio of 3/8 or more, such as RLL signals, is desired. Where plural signals each having a short recording wavelength and having large difference in the recording frequency between them are used, mere improvement of the electromagnetic characteristics of the magnetic layer in the manner as disclosed in JP-A-58-122623 and JP-A-61-74137 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") is limited and insufficient so as to sufficiently overwrite the signal with a short recording wavelength over the signal with a long recording wavelength.
This is because even though a shorter wavelength recording signal is overwritten over the previously recorded longer wavelength signal in the conventional magnetic layer having a thickness of 1.0 .mu.m or more, the magnetic force line of the shorter wavelength recording signal could not reach the deep area of the magnetic layer so that the previously recorded longer wavelength signal could not be erased.
With the elevation of the recording density in the current magnetic recording medium, the gap of the magnetic head to be applied thereto has become narrowed. Accordingly, sufficient recording in the direction of the thickness of the medium has become difficult.
In order to overcome the above-mentioned problems, if the magnetic layer is reduced to less than 1 .mu.m, the magnetic layer could easily be peeled off with dropout occurring. In addition, there are other problems such as that the running durability of the medium could not be ensured and the reliability of it lowers.
U.S. Pat. No. 4,952,444 (corresponding to JP-A-62-214513) discloses definition of the Young's Modulus of the non-magnetic layer to improve the running durability of the medium. However, if the thickness of the magnetic layer is further reduced to 0.6 .mu.m or less, the running durability of the medium cannot fully be satisfied only by the disclosed technique.